A forest is a natural ecosystem composed most notably of trees. Different types of forests are found across the planet. In one area, a forest may be dry with little vegetation. In another, a forest may contain large trees that grow quickly because of high rainfall. Different types of forests exist because they grow under different climates (Figure 1).

Another reason is that human activities have changed some of the forests. These activities include things like felling or planting trees. To better understand the different types of forests found across Earth, the scientists had to decide what was most important about those forest differences to study. In other words, to study the differences between forests across the planet, FAO had to determine how it would classify forests.

Before we learn how FAO classified the world’s forests, let’s think about the place on which these forests grow. What is this place called?

If you guessed Earth, you are right! We know that Earth spins on its axis and revolves around the sun (Figure 2).The area near the equator is closest to the sun. Because of this, Earth is warmest near the equator and coolest near the poles (Figure 3).

About 71 percent of Earth is covered with water, and most of this is ocean. The top level of any ocean is called sea level. The height of the land above sea level is called its elevation. At higher elevations, the climate is cooler (Figure 4).

Across Earth, different areas receive different amounts of rainfall. Plants need water to survive and have adapted over time to live with varying amounts of rainfall. Some plants, such as those in tropical rain forests, must have a lot of water to survive. Other plants, like those in deserts, do not need much water to survive. Desert plants have adapted to conserve the water they receive. Drier areas have fewer plants and trees. Some areas have no plants or trees at all.

The three things that we have just explored are latitude, elevation, and rainfall (Figures 3-6). These three things affect what kind of forest grows naturally in a particular area on Earth (Figures 5-7).

In addition to latitude, elevation, and rainfall, there is another influence on Earth’s forests. This influence is changing Earth’s forests, no matter where on Earth the forests are located. It was this influence FAO was most interested in understanding. What influence did the scientists want to understand?

If you guessed humans, you are right! FAO wanted to understand how forests are changing as a result of human activity. To understand how humans impact the world’s forests, the scientists classified forests into three categories (Table 1).

The scientists also wanted to estimate the area of forests being used to maintain a diversity of plant and animal species and the area of forests that are legally established and protected to maintain this diversity.

The world’s forests cover about 31 percent of Earth’s land area (Figure 8).

This is a little more than 4 billion hectares (Figures 9 and 10). More than half of the world’s forests are in the Russian Federation, Brazil, Canada, the United States of America, and China (Figure 11).

Of the world’s forests, 36 percent are primary forests. Primary forests, and in particular wet tropical forests, are the world’s most diverse forests. They have the greatest variety of plant and animal species.

The number of hectares of planted forests increased between 2000 and 2010. Planted forests now make up 7 percent of the world’s forests, or 264 million hectares. Of all the world’s forests, most are forests growing naturally without human assistance, but show signs of human activities. These forests make up 57 percent of the world’s forests (Figure 12).

Since 2000, about 13 million hectares of forest have been lost each year (Figure 13). While this is not good news, it is less than the rate of deforestation in the previous 10 years.

Forests are lost for a number of reasons. Trees are felled, for example, to clear land for agriculture or development. Extreme natural events such as tornados, hurricanes, volcanic eruptions and droughts also damage or destroy forests.

An area the size of Greece or Nicaragua is lost to deforestation every year. Not all countries, however, have fewer forests today than 10 years ago. Some countries have increased their forest areas and others have slowed the rate of forest loss.

To help understand more about the world’s forests’ gains and losses, look at figures 16-19. Figure 16 is a map you should recognize. This is a map of the world that shows each country at its normal size. Find your own country on the map. Figures 17-19 are called cartograms. Each country size in these cartograms is distorted to show forest growth or loss. If the forest growth or loss were the same in each country, each country would be the same size. In each cartogram, find your own country.